An underwater search has entered its second day as authorities continue to race the clock to find a black box flight recorder belonging to a missing Malaysia Airlines jet.

Co-ordinated by Australia, the search and rescue mission in the southern Indian Ocean, some 1700 kilometres southwest of Perth, continued on Saturday spanning an area of about 217,000 square kilometres.

The focus has turned to the work of Australian navy vessel Ocean Shield and the British oceanographic survey vessel HMS Echo, which deploy "pinger detectors" in an attempt to trace a signal from the black box.

But the battery on the black box beacon is expected to run out of power within days.

Above the waves an aerial search continues for debris from flight MH370.

Up to 10 military planes, three civil jets and 11 ships will search on Saturday.